The purpose of this investigation is to study metabolites, agents and conditions which affect the activity of the ATPase primarily located in the plasma membrane of the corneal endothelial cell. Emphasis will be placed on finding sulfhydryl locations in the plasma membranes, characterization of the ATPase in those membranes and the particular influence of glutathione, adenosine, insulin, cyclic AMP and cyclic GMP upon the activity of the ATPase. Impermeant maleimides will be used as a tool in locating plasma membrane sulfhydryl groups. Plasma membranes will be variously prepared: zinc ions, Tris and isopycnic centrifugation with a sucrose gradient. The activity of the ATPase will be assayed with ammonium molybdate and sulfonic acid for the release of inorganic phosphate.